Generally, in view of the physical aspect, an amorphous material is characterized by the absence of long-range order appeared from a crystal, even though there may be a certain regularity of the structure on a local scale, i.e., short-range order. Solids having isotropy may be made from the structurally disordered amorphous to provide different properties resulted from a wide range of composition. In addition, if energy is applied to the amorphous, the crystallization is achieved through primary phase transition. If bulky amorphous is crystallized by the nuclear generation and growth, the material is changed into polycrystalline material with different axial directions of grains.
The crystal axes of grains within bulky ceramic material bulky are respectively oriented toward a different direction. In order to employ the ceramics having a piezoelectric property as a piezoelectric device, a polarizing direction of grains within a sample has to be oriented toward any one direction as much as possible. A polling method applying a direct-current electric field as high as possible is employed to orient a polarization. A dimension of the electric field is various depending upon physical property of the sample; however, the electric field of a range from a few kV/mm to several dozens kV/mm is required. The material to which the above method is applied is mainly ferroelectrics. A coupling coefficient indicative of the piezoelectric characteristics depending upon the distributing degree of the polarizing direction is related to the dimension of the electric field and an average size of grains, but does not exert effect upon a value of signal crystal.
Accordingly, if the electric field is applied in one direction to the material having the piezoelectricity during the crystallization of the amorphous material, the energy affecting ions, atoms or molecules in the applying direction of the electric field is larger than that applied in other directions, leading elements to be more activated. The growth of the crystal is more activated in the direction that polarization easily occurs and the electric field is identical, than other axis.